This study was designed to compare the biomechanical effects of three posterior fixations for thoracolumbar burst fractures using the finite element (FE) method. Five T11-L1 FE models, including the intact, the fractured at T12, the monosegment fixated at the level of the fracture, the short-segment fixated with four pedicle screws and the short-segment fixated with five pedicle screws, were created. And four loading conditions (flexion, extension, lateral bending and torsion) were imposed on these models and deformations in these models under different loading conditions were calculated by finite element method. The biomechanical effects of the three different pedicle screw fixations for thoracolumbar burst fractures were compared and analyzed. The results showed that the displacement level in monosegment fixation model was close to that in the intact one. The extension motion was more limited in short-segment fixation models than that in monosegment fixation model. Under the lateral bending condition, the level of the displacements in these models were similar and the peak rotation angles in the three fixation models were close to that in the intact one. The displacements in fractured T12 were increased in monosegment fixation model under all loading conditions. These indicated that the monosegment fixation couldn’t provide desirable stability for the fractured T11-L1 and the short-segment fixation with five pedicle screws was the best selection because of ideal stability and movability.